Computational thermochemistry of C-nitroso compounds

The molecular structure and thermodynamic stability of C-nitroso and dinitroso (azodioxide) compounds (CNC) have been studied by using high-level, composite, ab initio method (G4MP2) via the series of appropriate homodesmotic, dimerization reactions. The calculated reaction enthalpies and Gibbs free energies allowed us to estimate relative stability of dinitroso moiety and the role of substituents in thermodynamic stabilization of dinitroso group versus its monomeric precursor. The stability of dinitroso compounds is generally low as is indicated by large positive values for standard enthalpies of formation. The stabilization of the dinitroso group is much more pronounced in alkyl, alkenyl, or alkynyl derivatives than in the aromatic derivatives. The thermodynamic stability of E-stereoisomers of dinitroso compounds is generally larger than their Z-stereoisomer analogues. However, the difference in E/Z stereoisomer stability is quite small in aromatic dinitroso compounds. We have discussed the influence of substituents on the molecular geometry of the nitroso and dinitroso groups. We have also discussed the nature and strengths of solid-state forces pertaining to CNC.     

Solution thermochemistry of diethyldithiocarbamato-iron(III)

The enthalpy change (303 K) for the standard state solid phase complexation reaction

is derived using conventional solution calorimetric techniques (ΔH°_R=?82.7±2.0 kJ mol^?1. Knowlege of ΔH°_R is a necessary pre-requisite for the future derivation of the FeS thermochemical bond energy.     

Computational thermochemistry of glycolaldehyde

We use a variant of the focal point analysis to refine estimates of the relative energies of the four low‐energy torsional conformers of glycolaldehyde. The most stable form is the cis‐cis structure which enjoys a degree of H‐bonding from hydroxyl H to carbonyl O; here dihedral angles τ₁ (O?C? C? O) and τ₂ (C? C? O? H) both are zero. We optimized structures in both CCSD(T)/aug‐cc‐pVDZ and aug‐cc‐pVTZ; the structures agree within 0.01 Å for bond lengths and 1.0 degrees for valence angles, but the larger basis brings the rotational constants closer to experimental values. According to our extrapolation of CCSD(T) energies evaluated in basis sets ranging to aug‐cc‐pVQZ the trans‐trans form (180°, 180°) has a relative energy of 12.6 kJ/mol. The trans‐gauche conformer (160°, ±75°) is situated at 13.9 kJ/mol and the cis‐trans form (0°, 180°) at 18.9 kJ/mol. Values are corrected for zero point vibrational energy by MP2/aug‐cc‐pVTZ frequencies. Modeling the vibrational spectra is best accomplished by MP2/aug‐cc‐pVTZ with anharmonic corrections. We compute the Watsonian parameters that define the theoretical vibrational‐rotational spectra for the four stable conformers, to assist the search for these species in the interstellar medium. Six transition states are located by G4 and CBS‐QB3 methods as well as extrapolation using energies for structures optimized in CCSD(T)/aug‐cc‐pVDZ structures. We use two isodesmic reactions with two well‐established thermochemical computational schemes G4 and CBS‐QB3 to estimate energy enthalpy and Gibbs energy of formation as well as the entropy of the gas phase system. Our extrapolated electronic energies of species appearing in the isodesmic reactions produce independent values of thermodynamic quantities consistent with G4 and CBS‐QB3. © 2013 Wiley Periodicals, Inc.     

Synergistic solvent extraction of Co(III) by thenoyltrifluoroacetone and some organophosphorus compounds

The extraction of Co(III) from aceticacid-acetate buffer solutions with various mixtures of ligands has been studied. Thenoyltrifluoroacetone mixed with triphenylphosphine oxide, trioctylphosphine oxide or tributyl phosphate were used as extractants. The effect of different parameters affecting the distribution ratio was studied in detail. Also, the corresponding thermodynamic parameters are calculated and discussed, together with the structures of extracted species.     

NMR study of monophthalocyaninatolanthanide (III) compounds

The variation of ¹H NMR shifts of monophthalocyaninatolanthanide (III) compounds of nine rare earth elements from Sm³⁺ to Lu³⁺ (except Gd³⁺) was studied. It was found that a “triad effect” appears in the sign alteration of the induced chemical shifts of α, β protons in the phthalocyanine rings for the second half of the rare earth series, that is, ¹H NMR spectra shift upfield for Tb³⁺, Dy³⁺ and Ho³⁺ compounds, while for Er³⁺, Tm³⁺ and Yb³⁺ the spectra shift downfield. The largest alteration of the chemical shifts appears in the compound with Tb³⁺. This is in agreement with the regularity obtained theoretically by Bleaney. The ¹³C NMR spectra of several monophthalocyaninatolanthanide compounds have also been recorded. The variation of the chemical shifts was discussed.     

稀土单酞菁化合物的NMR研究

研究了从Sm^3^+到Lu^3^+(Gd^3^+除外)九个稀土单酞菁化合物的^1H NMR化学位移.发现对重稀土化合物,酞菁环上α、β质子诱导位移符号的变化呈现"三个一组效应".即,"Tb^3^+、Dy^3^+、Ho^3^+化合物,^1H共振谱线移向高场,而对Er^3^+、Tm^+^3、Yb^3^+化合物,则移向低场.化学位移的最大变化发生在4f^8构型(Tb^3^+)处.所得结果与Bleaney理论一致.测得部分稀土单酞菁化合物的^1^3C NMR谱,讨论了化学位移的变化.     

Extraction of cadmium(II) by organophosphorus compounds

The extraction of cadmium(II) by di-(2-ethylhexyl) phosphoric acid dissolved in tetradecane from aqueous chloride and perchlorate solutions has been studied at 25°C. The distribution of the metal has been determined as a function of metal and DEHPA concentrations. Distribution data have been treated both graphically and numerically using the program LETAGROP-DISTR (Acta Chem. Scand. 1971, 25, 1521) and the composition of the extracted species into the organic phase has been determined. The extraction constants for these species are given in Table 1.     

Modeling the gas-phase thermochemistry of organosulfur compounds

Key to understanding the involvement of organosulfur compounds in a variety of radical chemistries, such as atmospheric chemistry, polymerization, pyrolysis, and so forth, is knowledge of their thermochemical properties. For organosulfur compounds and radicals, thermochemical data are, however, much less well documented than for hydrocarbons. The traditional recourse to the Benson group additivity method offers no solace since only a very limited number of group additivity values (GAVs) is available. In this work, CBS‐QB3 calculations augmented with 1D hindered rotor corrections for 122 organosulfur compounds and 45 organosulfur radicals were used to derive 93 Benson group additivity values, 18 ring‐strain corrections, 2 non‐nearest‐neighbor interactions, and 3 resonance corrections for standard enthalpies of formation, standard molar entropies, and heat capacities for organosulfur compounds and organosulfur radicals. The reported GAVs are consistent with previously reported GAVs for hydrocarbons and hydrocarbon radicals and include 77 contributions, among which 26 radical contributions, which, to the best of our knowledge, have not been reported before. The GAVs allow one to estimate the standard enthalpies of formation at 298 K, the standard entropies at 298 K, and standard heat capacities in the temperature range 300–1500 K for a large set of organosulfur compounds, that is, thiols, thioketons, polysulfides, alkylsulfides, thials, dithioates, and cyclic sulfur compounds. For a validation set of 26 organosulfur compounds, the mean absolute deviation between experimental and group additively modeled enthalpies of formation amounts to 1.9 kJ mol^?1. For an additional set of 14 organosulfur compounds, it was shown that the mean absolute deviations between calculated and group additively modeled standard entropies and heat capacities are restricted to 4 and 2 J mol^?1 K^?1, respectively. As an alternative to Benson GAVs, 26 new hydrogen‐bond increments are reported, which can also be useful for the prediction of radical thermochemistry.     

Vibrational zero point energy of organophosphorus(V) compounds

The calculation of vibrational zero-point energies (ZPEs) of organophosphorus(V) compounds is reported. The contributions of P O and PS bonds have been determined and incorporated in our empirical formula to estimate vibrational zero point energies of the investigated compounds. The calculated ZPEs for more than 80 organophosphorus compounds (V) containing these bonds correlate well with the reported available values. In addition, the comparison of these results with those obtained by quantum chemistry methods (HF/6-31G*, B3LYP/6-31G*) and by a similar empirical approach, indicates the reliability of our empirical model.     

(Chloromethyl)thallium(III) compounds

Aryl(chloromethyl)thallium chlorides, Ar(ClCH₂)TlCl (Ar=C₆H₅, p-CH₃C₆H₄) have been prepared by treatment of arylthallium dichlorides with diazomethane. The derived carboxylates, Ar(ClCH₂)TlX, react with HgX₂ to give the dicarboxylates, (ClCH₂)TlX₂ (X = OCOCH₃, OCOC₃H₇-i) and with tetramethyltin to give CH₃(ClCH₂)TlX compounds. R(ClCH₂)TIX compounds (R = CH₃, C₆H₅, p-CH₃C₆H₄) undergo disproportionation in methanol to R₂TlX and (ClCH₂)₂TlX compounds.     

Vibrational spectroscopic study of the structure of Ti(III) organometallic compounds

Conclusions A full interpretation was carried out for the vibrational spectra of TiR₃, where R= -CH₂C₆H₅, -CH₂C(CH₃)₂C₆H₅, and-CH₂Si(CH₃)₃. The absorption bands for the Ti-C bonds were delineated. A dimeric structure was established for the compounds studied with a Ti-Ti bond, whose band lies at 230–280 cm^–1. There is an interaction of the titanium atom with the -carbon atom of the ligand for the Ti(III) benzyl and neophyl derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2736–2739, December, 1987.     

Computational study of the thermal decomposition and the thermochemistry of allyl ethers and allyl sulfides

In spite of the several experimental and computational studies on the thermal decomposition of allyl ethers and allyl sulfides, there are still disagreements on aspects of the reaction mechanism, such as the true nature of the transition states and the grade of synchronicity of the reactions. This work presents a computational study of the gas-phase thermolysis reaction of allyl ethers and allyl sulfides substituted at α-carbon, at the M05-2X/6-31+G(d,p) level of theory and a temperature range from 586.15 to 673.15 K. The substituent groups were methyl, ethyl, n-propyl, i-propyl, allyl, benzyl and acetonyl. It was found that the sulfides react faster than the homologous ethers and that the substituent groups with the capacity of delocalize charge increase the reaction rate. Through natural bond orbital calculations, the transition states were characterized. The synchronicities and atomic charges of the studied reactions were determined. A computational study at the G3 level of theory on the thermochemistry of allyl ethers and sulfides was also carried out.     

Indium(III) coordination compounds

Data on the homo- and heteroleptic coordination compounds of indium(III) with halide, pseudo-halide, and N,O-donor ligands are generalized. Trends in the coordination numbers and coordination polyhedron geometries and the specifics of formation of hybrid polymer structures are considered. 182 references.     

Computational s-block thermochemistry with the correlation consistent composite approach

The correlation consistent composite approach (ccCA) is a model chemistry that has been shown to accurately compute gas-phase enthalpies of formation for alkali and alkaline earth metal oxides and hydroxides (Ho, D. S.; DeYonker, N. J.; Wilson, A. K.; Cundari, T. R. J. Phys. Chem. A 2006, 110, 9767).The ccCA results contrast to more widely used model chemistries where calculated enthalpies of formation for such species can be in error by up to 90 kcal mol-1. In this study, we have applied ccCA to a more general set of 42 s-block molecules and compared the ccCA DeltaHf values to values obtained using the G3 and G3B model chemistries. Included in this training set are water complexes such as Na(H2O)n+ where n = 1 - 4, dimers and trimers of ionic compounds such as (LiCl)2 and (LiCl)3, and the largest ccCA computation to date: Be(acac)2, BeC10H14O4. Problems with the G3 model chemistries seem to be isolated to metal-oxygen bonded systems and Be-containing systems, as G3 and G3B still perform quite well with a 2.7 and 2.6 kcal mol-1 mean absolute deviation (MAD), respectively, for gas-phase enthalpies of formation. The MAD of the ccCA is only 2.2 kcal mol-1 for enthalpies of formation (DeltaHf) for all compounds studied herein. While this MAD is roughly double that found for a ccCA study of >350 main group (i.e., p-block) compounds, it is commensurate with typical experimental uncertainties for s-block complexes. Some molecules where G3/G3B and ccCA computed DeltaHf values deviate significantly from experiment, such as (LiCl)3, NaCN, and MgF, are inviting candidates for new experimental and high-level theoretical studies.     

Synergistic solvent extraction of Eu(III) and Tb(III) with mixtures of various organophosphorus extractants

Synergistic solvent extraction of Eu(III) and Tb(III) from thiocyanate solutions with mixtures of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and di-2-ethylhexylphosphoric acid (DEHPA) or tributyl phosphate (TBP) or trioctylphosphine oxide (TOPO) or triphenylphosphine oxide (TPhPO) in benzene has been studied. The mechanism of extraction can be explained by a simple chemically based model presented in this paper. The equilibrium constants of the mixed-ligand species of the various neutral donors have been determined by non-linear regression analysis.     

Oxidimetric determination of some compounds with hexamminecobalt(III) tricarbonatocobaltate(III)

The possibilities of utilization of the hexamminecobalt(III) tricarbonatocobaltate(III) complex for potentiometric determination of some substances are discussed. The reaction scheme for this reagent is proposed for acidic media (the “generation” of Co³⁺). A microdetermination of iodide has been developed. The oxidation of thiocyanate, thiosulfate and hydrogen peroxide is briefly discussed.     

Thermodynamic properties of lanthanum(III) and holmium(III) hydroxo compounds

Conductometric and potentiometric titration experiments were performed to determine the pH values of hydroxo compound formation in solutions of lanthanum(III) and holmium(III) nitrates. The instability constants of monohydroxo complexes, the solubility product constants of hydroxides, and the Gibbs energies of formation of the corresponding compounds are calculated.